The Program for Pandemic Preparedness through Ventilation, P3Venti, leads, collects and distributes scientific research on the influence and potential impact of ventilation on aerogenic pathogen spread, exposure risk and infection control.
P3Venti has an expected duration of three years (August 2022 – July 2025), is coordinated by TNO, and carried out by a consortium of research institutes and partners financed by the Dutch ministry of health (VWS).
For more in-depth information on the program, please refer to the program summary.
The goal of P3Venti is to support the government and (not-for-profit) stakeholders in their policy and decision making by generating scientific, actionable knowledge. Three key areas can be identified in this task:
A critical part of P3Venti is fundamental scientific research. Scientific publications will be collected on a database on this website as they are published.
Our research aims to build knowledge in several key areas:
This research includes studying exposure risks and the effect of ventilation measures, observations in operational conditions such as elderly care homes, interviews with stakeholders and occupants, computer modeling and experimental particle dispersion and airflow vector research both in a mock-up and in-situ.
Knowledge from the other two areas is collected and combined with social-scientific methods to better transfer the knowledge to, and facilitate the implementation of measures for the users.
Investigation of viability and infectivity of virus-bearing particles (especially related to SARS-CoV-2) in relation to time and size distribution. Focus on literature studies and experimental research.
To ensure the accessibility and dissemination of the scientific findings and knowledge, P3Venti is establishing a knowledge network.
The core of the knowledge network are the members of a broad scientific sounding board, and the researchers within the program. From this core, the network will expand and grow as the program matures, facilitating partnerships and collaboration between related scientific programs and projects, such as PDPC, CLAIRE and MIST; as well as promoting collaboration and feedback with healthcare institutions and regulatory bodies.
With this network, P3Venti not only provides answers to the specific research questions defined for this program, but also contributes to the strengthening of the knowledge base needed to identify and effectively address new research questions and needs in a timely manner.
The network will increasingly expand to include delegated professionals connected to long-term care and possibly from other social sectors. As such, P3Venti is actively looking to make national and international connections with interested scientists and organizations to start exchanging knowledge and expertise. In this spirit, we would like to invite and encourage you to reach out and contact us if you have any interest in joining the Network by attending our symposium, joining our LinkedIn group, following the LinkedIn information page, or sending any questions to firstname.lastname@example.org.
An initial overview of current key players within the knowledge network can be found on the network page.
Based on the knowledge gained and collected through P3Venti, we strive to provide practical measures, methods and guidelines to help healthcare institutions and regulatory bodies to be better prepared for the next pandemic. A vital aspect is to as much as possible ensure healthy and enjoyable living conditions under these measures. Here you can find questions, answers and tips on how ventilation and air purification can contribute to reducing the spread of viruses through the air.
Ventilation can reduce the concentration of aerosols (small airborne particles) – and therefore viruses - in a space. However, the way most buildings are currently ventilated will have little to no effect when the source of the aerosols and the receiver (person) are close to each other. In addition, very large particles (larger than 100µm) will hardly be influenced by air currents, so their behaviour is more dependent on gravitational effects. Ventilation can contribute in particular to reducing the concentration of mostly smaller particles that travel and spread over longer distances. However, this is subject to the certain important conditions.
As much as possible, try and avoid the recirculation of air throughout multiple spaces (whereby air is extracted from one space to be supplied to another). The application of recirculating units within the same space for (additional) heating and/or cooling is not a problem as long as enough fresh air is supplied (ventilation). Virus particles will spread throughout the space regardless of recirculating units, which through additional mixing only shorten the time needed for these particles to spread. Important to note is that strong air currents greatly increase the distance exhalations (particle clouds/plumes) travel through the air. Through this route, other people in the room could potentially be infected over distances exceeding 1.5m.
The recirculation of air across multiple spaces in a building is a system that is rarely used in the Netherlands and, if so, almost exclusively in older buildings. With a sufficient supply of fresh air, the natural dilution or removal of particles through ventilation is adequate, so this may not be a problem. In buildings with increased amounts of infected individuals and/or ‘corona risk-groups’ (cohorts), these recirculation mechanisms are best not used. In these cases it is better to exclusively use fresh air supply for ventilation to answer to the need of preventing avoidable ‘risks’.
An important aspect for the effectiveness of ventilation systems is ensuring their proper use. If a ventilation system is not used or maintained properly, the intended and potential effect cannot be reached. The website www.ventilerenzogedaan.nl provides several tips for the correct use of ventilation systems.
Several studies have shown that virus particles can travel through the air inside aerosols. It has also been found that these virus particles can continue to be infectious at relatively long distances from their source (approximately 2 meters), and can thus potentially leadto infection.1 However, based on the current state of research, the extent to which ventilation reduces the risk of infection cannot be determined. In a recent study conducted in 10,000 classrooms in the Italian region of De Marke, the likelihood of infection in a mechanically ventilated room was 74% lower than in a naturally ventilated room.2 During this study, the students wore face masks at school, including while they were in the classrooms. By implementing this personal protection measure, the contribution of short-distance transmission was likely limited, while potentially increasing the role of long-distance transmission. It should be noted that this study was limited in its methods to control for key confounding factors in the analysis.
The question that arises now is to what extent the aerogenic transmission route contributes to the occurrence of an infection at longer distances and what role the ventilation system plays in this.3–14 In a study by Peng et al., various Covid-19 outbreaks were modelled and compared with known pathogens such as measles and tuberculosis, the aerogenic transmission characteristics of which are well-documented. This suggests that Covid-19 can also be considered aerogenic.15 However, the discussion regarding the contribution of this route at short and long distances continues.
The concentration of virus particles is highest near the source, regardless of particle size, particularly in exhaled air.16 Social distancing is an effective way to reduce the risk of infection.17 However, scientific literature does not provide a clear view regarding the size of particle released during respiratory activities such as breathing, talking, singing, sneezing, and coughing. These includes small particles (< 5 µm), larger particles (> 100 µm) and all particles sizes in between. It does seem that the number of emitted particles is proportional to the sound level produced during the respiratory activity (volume).18 It is also evident that current ventilation solutions have little effect on short-distance transmission (close to the source).
Indoor relative humidity and temperature play a role in the airborne spread of certain particle sizes.19 At lower relative humidities (already below 80%), particles ≤ 40 µm will rapidly decrease in size and weight due to evaporation, after which they can be carried much further by an air current. For particles ≥ 80 µm, this effect seems negligible.20 However, there are also indications that virus particles in aerosols of 5-10 µm are deactivated more quickly at lower relative humidity (<45%).21 Temperature differences (between indoor and outdoor) also affect natural ventilation and consequently particle spread, especially in the case of single-sided ventilation (where ventilation facilities are located in only one façade).22According to an expert panel, controlling the relative humidity and temperature is considered less effective and feasible for reducing the risk of infection.19
By introducing clean outdoor air (ventilation), the concentration of aerosols can be diluted, reducing the risk of infection through airborne particles.17 Several studies accordingly consider ventilation to be an efficient, feasible, and acceptable intervention to reduce the risk of infection through the aerogenic route.19 The time needed to lower particle concentration (flush time) is also important. For example, ventilation may be ineffective if a space is in continuous use with a rapid throughput of people, such as in a busy (enclosed) toilet cubicle.23 Combining ventilation with other methods (such as masks or air filters) was found in a computational study to be the most effective measure for reducing the risk of infection.22 Additionally, it should be noted that ventilation can negatively impact the indoor thermal and acoustic comfort.26 Determining the effectiveness of ventilation and (pathogenic) particle removal from the space, the so-called 'ventilation effectiveness' or 'contaminant removal efficiency', is an important parameter- in this regard.24,25
In addition to the amount of fresh outdoor air, which in theory has a low concentration of virus particles, the distribution and movement of air throughout the space is important. With an uneven distribution of supplied air, certain parts of the space may be well ventilated while others may not. This can result in situations where the ventilation system contributes to a reduction in concentration in one part of the room while having much less of an effect in another part.
Computational research has indicated that the difference between no ventilation and some ventilation is most significant.27 In other words, if there is already adequate ventilation, further increasing it may not contribute much.27,28 There is no known specific amount of ventilation that can bring the number of aerogenic infections to an acceptable level. Beside the discussion of what is 'acceptable,' this depends, among other factors, on the infectivity of the pathogen. For instance, the Omicron variant is more contagious than the Delta variant of the SARS-CoV-2 virus. The study by Jia et al. suggests a value of 10 l/s/person is necessary for short and long-distance exposure to create a situation comparable to the outdoors.29 This quantity is somewhat higher than what is generally specified in the current Dutch Building Code (Bouwbesluit) 2012. However, research by Bartels et al. shows that there seems to be no direct reason to adjust these ventilation requirements.27
1. Lednicky JA, Lauzardo M, Hugh Fan Z, et al. Viable SARS-CoV-2 in the air of a hospital room with COVID-19 patients. Int J Infect Dis. 2020;(1):1-20. doi:10.1016/j.ijid.2020.09.025
2. Buonanno G, Ricolfi L, Morawska L, Stabile L. Increasing ventilation reduces SARS-CoV-2 airborne transmission in schools: a retrospective cohort study in Italy’s Marche region. Front public Heal. Published online 2022:1-14.
3. Liu YY, Ning Z, Chen Y, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. 2020;86(21):2020.03.08.982637. doi:10.1101/2020.03.08.982637
4. Cowling BJ, Ip DKM, Fang VJ, et al. Aerosol transmission is an important mode of influenza A virus spread. Published online 2013:1-12. doi:10.1038/ncomms2922.Aerosol
5. WHO. Modes of transmission of virus causing COVID-19 : implications for IPC precaution recommendations. Sci Br WHO. 2020;(March):10-12. doi:10.1056/NEJMoa2001316.5.
6. Fennelly KP. Particle sizes of infectious aerosols: implications for infection control. Lancet Respir Med. 2020;8(9):914-924. doi:10.1016/S2213-2600(20)30323-4
7. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis. 2006;12(11):1657-1662. doi:10.3201/eid1211.060426
8. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11(10). doi:10.3390/v11100940
9. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One. 2012;7(4). doi:10.1371/journal.pone.0035797
10. Li Y, Huang X, Yu ITS, Wong TW, Qian H. Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air. 2005;15(2):83-95. doi:10.1111/j.1600-0668.2004.00317.x
11. Grosskopf K, Mousavi E. Bioaerosols in health-care environments. ASHRAE J. 2014;56(8):22-31.
12. Lindsley WG, Blachere FM, Thewlis RE, et al. Measurements of airborne influenza virus in aerosol particles from human coughs. PLoS One. 2010;5(11). doi:10.1371/journal.pone.0015100
13. Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S. Transmission routes of respiratory viruses among humans. Curr Opin Virol. 2018;28:142-151. doi:10.1016/j.coviro.2018.01.001
14. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of Respiratory Viral Infections. Annu Rev Virol. Published online 2020:1-19. doi:10.1146/annurev-virology-012420-022445
15. Peng Z, Rojas ALP, Kropff E, et al. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. Environ Sci Technol. 2022;56(2):1125-1137. doi:10.1021/acs.est.1c06531
16. Jones NR, Qureshi ZU, Temple RJ, Larwood JPJ, Greenhalgh T. Two metres or one : what is the evidence for physical distancing in past viruses , argue Nicholas R Jones and colleagues. Published online 2020:1-6. doi:10.1136/bmj.m3223
17. Chen W, Qian H, Zhang N, Liu F, Liu L, Li Y. Extended short-range airborne transmission of respiratory infections. J Hazard Mater. 2022;422(June 2021):126837. doi:10.1016/j.jhazmat.2021.126837
18. Jacobs P, Borsboom W. 2020 R11031 Ventilatie in Gebouwen En de Invloed Op de Verspreiding van COVID-19.; 2020.
19. de Crane D’Heysselaer S, Parisi G, Lisson M, et al. Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2. Pathogens. 2023;12(3):1-27. doi:10.3390/pathogens12030382
20. Kompatscher K, Traversari R. TNO 2020 R11208 Rev. 1. Literatuurstudie Naar de Afstand Die Deeltjes (>5 Μm) Afleggen Bij Verschillende Respiratoire Activiteiten.; 2020.
21. Oswin HP, Haddrell AE, Otero-Fernandez M, et al. The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment. Proc Natl Acad Sci U S A. 2022;119(27):1-11. doi:10.1073/pnas.2200109119
22. Villers J, Henriques A, Calarco S, et al. SARS-CoV-2 aerosol transmission in schools: The effectiveness of different interventions. Swiss Med Wkly. 2022;152(21-22):1-17. doi:10.4414/smw.2022.w30178
23. Denpetkul T, Pumkaew M, Sittipunsakda O, Leaungwutiwong P, Mongkolsuk S, Sirikanchana K. Effects of face masks and ventilation on the risk of SARS-CoV-2 respiratory transmission in public toilets: a quantitative microbial risk assessment. J Water Health. 2022;20(2):300-313. doi:10.2166/WH.2022.190
24. Mundt E, Mathisen HM, Nielsen P V., Moser A. REVHA Guidebook No 2 - Ventilation Effectiveness.; 2004.
25. NEN. NEN-EN-ISO 14644-3: Cleanrooms and associated controlled environments - Part 3: Test methods. Published online 2019.
26. de la Hoz-Torres ML, Aguilar AJ, Costa N, Arezes P, Ruiz DP, Martínez-Aires MD. Reopening higher education buildings in post-epidemic COVID-19 scenario: monitoring and assessment of indoor environmental quality after implementing ventilation protocols in Spain and Portugal. Indoor Air. 2022;32(5):282. doi:10.1111/ina.13040
27. Bartels AA. Effect-van-Verschillende-Ventilatiehoeveelheden-Op-Aerogene-Transmissie-van-Sars-Cov-2. Risicoschatting Op Basis van Het AirCoV2-Model.; 2020.
28. Rocha-Melogno L, Crank K, Bergin MH, Gray GC, Bibby K, Deshusses MA. Quantitative risk assessment of COVID-19 aerosol transmission indoors: a mechanistic stochastic web application. Environ Technol. 2023;44(9):1201-1212. doi:10.1080/09593330.2021.1998228
29. Jia W, Wei J, Cheng P, Wang Q, Li Y. Exposure and respiratory infection risk via the short-range airborne route. Build Environ. 2022;219(April):109166. doi:10.1016/j.buildenv.2022.109166
In laboratory studies air purification methods seem to be effective in reducing virus particle counts. These air purifiers often also reduce the concentration of particles in a space. However, there is a very limited number of studies showing, in practice, the effectiveness of air purifiers in reducing the chance to be infected with respiratory viruses. Based on this knowledge it is not recommended to trust solely on air purification methods to limit aerogenic transmission risks. The ventilation system should be functioning properly before considering supplementing it with air purification methods. The effectiveness of these methods has been minimally studied or demonstrated in operational conditions, especially concerning the inactivation or transmission of viruses like SARS-CoV-2. Current air purification methods, much like ventilation, will have little to no impact on situations where the particle source and recipient are in close proximity.
When implementing air purification, it's important to be aware of potential negative health effects from prolonged exposure to emitted by-products (such as ozone and potentially UVC).
Air purification equipment is often used to reduce indoor particle concentrations. This equipment improves air quality through filtering, and through its potential to remove or deactivate/kill microbiological contaminants (bacteria, viruses, fungi).1,2 The SARS-CoV-2 pandemic has brought attention to virus inactivation and virus particle removal as important topics. As a result, the use of technologies such as UV and ionization for air purification is gaining attention. However, the effectiveness of these technologies varies widely, and there is limited practical, in-situ research.3,4
Many studies are available that examine filtration, UV, or ionization as purification technologies. Filtration studies, mostly focus on filtering certain particle sizes The neutralisation of microorganisms has received little attention, specifically the inactivation of viruses. The vast majority of studies on UV and ionization conclude that more research is needed to determine the mechanisms and effectiveness of air purification technology for specific microbiological contaminants. Scientific studies do not show consensus in findings regarding effectiveness.1,2,5–11Air purification has also rarely been investigated in practical settings regarding respiratory viruses.11–16 Two such practical studies examining the effect of air purifiers on viral transmission (actual occurrences of infections) found the purification technology to have no effect.11,14 Laboratory studies are being conducted wherein cultured microorganisms are exposed to UV. The extent to which this inactivates or neutralises the microorganism provides information about its sensitivity to UV. Nebulising microorganisms is more accurate when simulating real situations for practical experiments. The effect is measured by monitoring the decrease in the airborne particle count over time. This method can provide information on filtering ability, but not on the inactivation effectiveness of microorganisms. Methods to determine this inactivation effectiveness exist, but were rarely applied in the examined literature. The effects of constant and intermittent particle sources have not been included in these studies. The assumption is often a one-time emission at the start of the experiment, which is a poor approximation of real situations.
Ionization technologies are studied in relation to non-pathogenic particles. Studies on the effectiveness of ionization regarding the inactivation of microbiological contaminants are scarce.12,17–19 The same is true for practical/in-situ studies.20–23 The few available studies do not draw conclusions about the inactivation of microbiological contaminants or the effectiveness of a specific air purifier.
Studies examining prolonged exposure to UV or by-products released during photocatalytic oxidation (PCO) or ionizing technologies are scarce. Publications do indicate that most commercially available air purifiers emit by-products, although these can vary significantly from the manufacturers stated values. In general, it is advisable to test air purifiers thoroughly based on UV and ionization for by-products. In several European countries, this is common practice or even legally required before they can be used in public spaces. There is literature that suggests that high levels of exposure to electrons released during ionization can lead to negative health effects. Therefore, there may be potential implications related to prolonged exposure to these air purification technologies.
So-called far-UVC lamps with a wavelength of 222 nm are said to be as effective in inactivating viruses as the usual 254 nm. They are also said to produce fewer chemical by-products in moderately to well-ventilated spaces.24 For this reason, UV lamps with a wavelength of 222nm are considered to be safe when used with people present.25 However, there is still insufficient research on the health effects of direct exposure to far-UVC, so the RIVM currently counsels against its use.26 Further research on the release and (prolonged) exposure to (far-)UVC, ozone, released radicals, and ionizing particles on human health is advised.13,27–34
Based on the available literature as well as the varying quality of these studies, no unequivocal conclusions can be drawn regarding the effectiveness of the investigated air purification technologies.4 Therefore, it is recommended to prioritize having adequate ventilation.
1. Liu DT, Phillips KM, Speth MM, Besser G, Mueller CA, Sedaghat AR. Portable HEPA Purifiers to Eliminate Airborne SARS-CoV-2: A Systematic Review. Otolaryngol - Head Neck Surg (United States). 2022;166(4):615-622. doi:10.1177/01945998211022636
2. Mahmoudi A, Tavakoly Sany SB, Ahari Salmasi M, et al. Application of nanotechnology in air purifiers as a viable approach to protect against Corona virus. IET Nanobiotechnology. 2023;(March):289-301. doi:10.1049/nbt2.12132
3. Vermeulen L, Bartels A. Meerwaarde van mobiele luchtreinigers in verminderen van transmissie van SARS-CoV-2 – een literatuurstudie. Published online September 2022. doi:10.21945/RIVM-2022-0134
4. Kompatscher K, Traversari R. Literatuurstudie Naar de Toepassing van Verschillende Luchtreinigingsmethoden Voor Inactivatie van Microbiologische Verontreinigingen.; 2022.
5. Bedell K, Buchaklian A, Perlman S. Efficacy of an automated multi-emitter whole room UV-C disinfection system against Coronaviruses MHV and MERS-CoV. Infect Control Hosp Epidemiol. 2017;37(5):598-599. doi:doi:10.1017/ice.2015.348
6. Green CF, Scarpino P V. The use of ultraviolet germicidal irradiation (UVGI) in disinfection of airborne bacteria. Environ Eng Policy. 2001;3(1):101-107. doi:10.1007/s100220100046
7. Jelden KC, Gibbs SG, Smith PW, et al. Ultraviolet (UV)-reflective paint with ultraviolet germicidal irradiation (UVGI) improves decontamination of nosocomial bacteria on hospital room surfaces. J Occup Environ Hyg. 2017;14(6):456-460. doi:10.1080/15459624.2017.1296231
8. Ko G, First MW, Burge HA. The characterization of upper-room ultraviolet germicidal irradiation in inactivating airbone microorganisms. Environ Health Perspect. 2002;110(1):95-101. doi:10.1289/ehp.0211095
9. Lin WE, Mubareka S, Guo Q, Steinhoff A, Scott JA, Savory E. Pulsed ultraviolet light decontamination of virus-laden airstreams. Aerosol Sci Technol. 2017;51(5):554-563. doi:10.1080/02786826.2017.1280128
10. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018;8(1):1-7. doi:10.1038/s41598-018-21058-w
11. Banholzer N, Zürcher K, Jent P, et al. SARS-CoV-2 transmission with and without mask wearing or air cleaners in schools in Switzerland: A modeling study of epidemiological, environmental, and molecular data. PLoS Med. 2023;20(5):e1004226. doi:10.1371/journal.pmed.1004226
12. Thornton GM, Fleck BA, Dandnayak D, Kroeker E, Zhong L, Hartling L. The impact of heating, ventilation and air conditioning (HVAC) design features on the transmission of viruses, including the 2019 novel coronavirus (COVID-19): A systematic review of humidity. PLoS One. 2022;17(10 October):1-23. doi:10.1371/journal.pone.0275654
13. Menzies D, Popa J, Hanley JA, Rand T, Milton DK. Effect of ultraviolet germicidal lights installed in office ventilation systems on workers’ health and wellbeing: Double-blind multiple crossover trial. Lancet. 2003;362(9398):1785-1791. doi:10.1016/S0140-6736(03)14897-0
14. Su C, Lau J, Gibbs SG. Student absenteeism and the comparisons of two sampling procedures for culturable bioaerosol measurement in classrooms with and without upper room ultraviolet germicidal irradiation devices. Indoor Built Environ. 2016;25(3):551-562. doi:10.1177/1420326X14562257
15. Hofbauer WK, Baßler M. Efficiency of UVC radiation as an air disinfectant in a real environment. In: Indoor Air. ; 2022.
16. Lindblad M, Tano E, Lindahl C, Huss F. Ultraviolet-C decontamination of a hospital room: Amount of UV light needed. Burns. 2020;46(4):842-849. doi:10.1016/j.burns.2019.10.004
17. Hagbom M, Nordgren J, Nybom R, Hedlund KO, Wigzell H, Svensson L. Ionizing air affects influenza virus infectivity and prevents airborne-transmission. Sci Rep. 2015;5:1-10. doi:10.1038/srep11431
18. Hyun J, Lee SG, Hwang J. Application of corona discharge-generated air ions for filtration of aerosolized virus and inactivation of filtered virus. J Aerosol Sci. 2017;107(August 2016):31-40. doi:10.1016/j.jaerosci.2017.02.004
19. Xu Y, Zheng C, Liu Z, Yan K. Electrostatic precipitation of airborne bio-aerosols. J Electrostat. 2013;71(3):204-207. doi:10.1016/j.elstat.2012.11.029
20. Bergeron V, Reboux G, Poirot JL, Laudinet N. Decreasing Airborne Contamination Levels in High-Risk Hospital Areas Using a Novel Mobile Air-Treatment Unit. Infect Control Hosp Epidemiol. 2007;28(10):1181-1186. doi:10.1086/520733
21. Meschke S, Smith BD, Yost M, et al. The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria. J Appl Microbiol. 2009;106(4):1133-1139. doi:10.1111/j.1365-2672.2008.04078.x
22. Xia T, Lin Z, Lee EM, Melotti K, Rohde M, Clack HL. Field Operations of a Pilot Scale Packed-bed Non-thermal Plasma (NTP) Reactor Installed at a Pig Barn on a Michigan Farm to Inactivate Airborne Viruses. 2019 IEEE Ind Appl Soc Annu Meet IAS 2019. Published online 2019:7-10. doi:10.1109/IAS.2019.8912457
23. Fennelly M, O’Connor DJ, Hellebust S, et al. Effectiveness of a plasma treatment device on microbial air quality in a hospital ward, monitored by culture. J Hosp Infect. 2021;108:109-112. doi:10.1016/J.JHIN.2020.11.006
24. Peng Z, Miller SL, Jimenez JL. Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps. Environ Sci Technol Lett. 2023;10(1):6-13. doi:10.1021/acs.estlett.2c00599
25. Pereira AR, Braga DFO, Vassal M, Gomes IB, Simões M. Ultraviolet C irradiation: A promising approach for the disinfection of public spaces? Sci Total Environ. 2023;879(December 2022). doi:10.1016/j.scitotenv.2023.163007
26. den Outer P, van Dijk A, Siegersma D, Hagens W. 2021-0050/VLH/WH Notitie UVC En Gezondheid.; 2021.
27. Medical Advisory Secretariat. Air Cleaning Technologies: An Evidence-Based Analysis. Vol 5.; 2005.
28. Jiang SY, Ma A, Ramachandran S. Negative air ions and their effects on human health and air quality improvement. Int J Mol Sci. 2018;19(10). doi:10.3390/ijms19102966
29. Cheek E, Guercio V, Shrubsole C, Dimitroulopoulou S. Portable air purification: review of impacts on indoor air quality and health. Sci Total Environ. Published online 2020:142585. doi:10.1016/j.scitotenv.2020.142585
30. Rijksinstituut voor Volksgezondheid en Milieu. Ionisatoren En Gezondheid.; 2010.
31. Blackhall K, Appleton S, Cates CJ. Ionisers for chronic asthma. Cochrane Database Syst Rev. 2012;(9). doi:10.1002/14651858.CD002986.pub2
32. Alexander DD, Bailey WH, Perez V, Mitchell ME, Su S. Air ions and respiratory function outcomes: A comprehensive review. J Negat Results Biomed. 2013;12(1):1. doi:10.1186/1477-5751-12-14
33. Liu S, Huang Q, Wu Y, et al. Metabolic linkages between indoor negative air ions, particulate matter and cardiorespiratory function: A randomized, double-blind crossover study among children. Environ Int. 2020;138(March):105663. doi:10.1016/j.envint.2020.105663
34. World Health Organization. Ultraviolet Radiation As a Hazard in the Workplace. World Heal Organ. Published online 2003.
Within an acceptable level of estimated risk, there is no immediate reason to deviate from the requirements for new construction outlined in the 2012 ‘Bouwbesluit’ (building code). However, it may be worthwhile to consider higher standards depending on the residents' susceptibility to infection. The 2012 Bouwbesluit ventilation requirement for new-build healthcare buildings is a minimum of 6.5 dm3/s per person. For healthcare bed areas, a fresh air supply of at least 12 dm3/s per person is required.
There are no scientific publications describing the effect of supplying a specific volume of air (ventilation) on the number of potential infections transmitted in a space, or the required degree of ventilation to achieve widely accepted infection levels. However, there are various guidelines, including those from the WHO and CDC, which provide recommended volumes of fresh outdoor air.1,2 The WHO guideline recommends 60 dm3/s per person for healthcare settings. This is significantly higher than the new-build requirements in the 2012 Dutch Building Code (Bouwbesluit). The Bouwbesluit 2012 stipulates a requirement of 0.9 dm3/s per m2 of floor area, with a minimum of 7 dm3/s per person for newly built habitable rooms in residential settings. Regarding healthcare, a threshold value of 12 dm3/s per person in bed areas and 6.5 dm3/s per person in other living areas is given.3
The WHO roadmap was developed after an exploratory study of available literature and an assessment of available guidelines on building ventilation. The literature included in the study seems not to contain research specifically focused on the spread of viruses.1 Recently, The Lancet COVID-19 Commission published a report proposing Non-infectious Air Delivery Rates (NADR) to limit the risk of aerogenic respiratory infections. For schools, offices, and vehicles, a range is recommended from good (10 l/s/person) to best (>14 l/s/person).4
1. WHO. Roadmap to Improve and Ensure Good Indoor Ventilation in the Context of COVID-19.; 2021.
2. de Crane D’Heysselaer S, Parisi G, Lisson M, et al. Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2. Pathogens. 2023;12(3):1-27. doi:10.3390/pathogens12030382
3. Bouwbesluit Online.
4. Allen JG. Proposed Non-infectious Air Delivery Rates ( NADR ) for Reducing Exposure to Airborne Respiratory Infectious Diseases Task Force Members. Lancet. 2022;(November):1-33.
People can be infected via three routes:
Human-to-human at close range by "direct contact"
By short- and long-range transmission via small droplets (aerosols) containing virus particles (the aerogenic route)
By indirect transmission via surfaces
Ventilation and air purification can potentially reduce the risk of infection through aerosols. For reference, see the question: "Can I reduce infections with ventilation?". Current common solutions for ventilation and air purification have little effect on short-range exposure, but these may contribute to reducing the risk for exposure at longer distances. It is currently unclear what proportion of infections occur by which transmission route.
The effect of continuously cleaning surfaces to prevent the risk of SARS-CoV-2 infections seems limited.
Viruses have three potential transmission routes:
Human-to-human at close range by "direct contact".
By short- and long-range airborne transmission via small or large droplets (aerosols) containing virus particles (the aerogenic route).
By indirect transmission via surfaces (from person to a surface to another person).1,2
The short- and long range aerogenic transmission routes are shown in Figure 1.
Figure 1 Transmission of SARS-CoV-2 via the air; Source: Jimenez.3
Transmission of the SARS-CoV-2 virus (and other viruses) primarily occurs at short distances through droplets and aerosols generated by various respiratory functions like breathing, talking, coughing, and sneezing.4–15 The resulting sound levels of these respirations is related to the amount of particles generated. The amount of time between infection and droplet generation plays an important role in the quantity of virus particles present in the exhaled aerosols.16 The available literature on the topic consistently finds a higher risk of transmission at short distances. Well-known guidelines, such as the 1.5-meter directive from institutions like the RIVM, have been designed with this in mind.
Originally, direct transmission through large droplets was considered the primary route for infection. However, increasingly this perspective is being critically examined and challenged, as aerosols can play an important role in viral transmission at short distances too. 17–20 Beside posing a risk at short distances, aerogenic transmission (by aerosol) can also occur over longer distances. Due to their small size, these aerosols can spread through the air and thus throughout a space.1,21 There is an increasing amount of literature that examines the aerogenic transmission route. 18,21 Some studies indicate that infections have occurred through the aerogenic route.18 However, collecting direct evidence exclusively for the aerogenic route is very challenging. Currently, it is not possible to determine the degree to which specific transmission routes contribute to infections. In other words, it is unknown what fraction of infections occurs via the aerogenic route, both at short and long distances. Conversely, it is also unknown what portion of infections occurs through other routes. 1,4,11,13,22–31
The third and final known infection route is indirect transmission of a virus via surfaces and hand contact. Scientific consensus and insights regarding this transmission route are mainly derived from research on other respiratory viruses.
Virus-containing droplets and particles settle on surfaces. The SARS-CoV-2 virus can remain infectious on a surface for several days 32–34 After contact with this surface, virus particles can subsequently be transmitted from hands to the mouth, nose or eyes (mucous membranes), leading to infection. While the importance of this route is confirmed by the literature, the extent to which it contributes to the occurrence of infections is not known.1,5,26,35–42 The CDC considers the chance of infection with the SARS-CoV-2 virus through this last route to be small.43,44
Furthermore, some literature has found that SARS-CoV-2 virus particles settled on surfaces can be inactivated through exposure to UV-C light.45–47,48 UV-C light might therefore be used for disinfecting surfaces. However, it should be noted that UV-C is harmful to humans, and indoor surface disinfection should only be performed when no individuals are present. Additionally, the effectiveness of this virus inactivation method is highly dependent on the UV-C exposure dose, time, and other conditions. For example, in outdoor settings, sunlight can deactivate the SARS-CoV-2 virus within 20 minutes.49
1. WHO. Modes of transmission of virus causing COVID-19 : implications for IPC precaution recommendations. Sci Br WHO. 2020;(March):10-12. doi:10.1056/NEJMoa2001316.5.
2. RIVM. Richtlijn COVID-19. 23 november.
3. Jimenez JL, Marr LC, Randall K, Ewing ET, Tufekci Z, Greenhalgh T. What Were the Historical Reasons for the Resistance to Recognizing Airborne Transmission during the COVID-19 Pandemic ? SSRN Electron J. 2021;(May):1-18. doi:10.1111/ina.13070
4. Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S. Transmission routes of respiratory viruses among humans. Curr Opin Virol. 2018;28:142-151. doi:10.1016/j.coviro.2018.01.001
5. da Silvia GM. An analysis of the transmission modes of COVID-19 in light of the concepts of Indoor Air Quality. :1-12.
6. Gralton J, Tovey ER, Mclaws ML, Rawlinson WD. Respiratory virus RNA is detectable in airborne and droplet particles. J Med Virol. 2013;85(12):2151-2159. doi:10.1002/jmv.23698
7. Asadi S, Wexler AS, Cappa CD, Barreda S, Bouvier NM, Ristenpart WD. Aerosol emission and superemission during human speech increase with voice loudness. Sci Rep. 2019;9(1):1-10. doi:10.1038/s41598-019-38808-z
8. Morawska L, Johnson GR, Ristovski ZD, et al. Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. J Aerosol Sci. 2009;40(3):256-269. doi:10.1016/j.jaerosci.2008.11.002
9. Stadnytskyi V, Bax CE, Bax A, Anfinrud P. The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission. Proc Natl Acad Sci U S A. 2020;117(22):19-21. doi:10.1073/pnas.2006874117
10. Qian H, Zheng X. Ventilation control for airborne transmission of human exhaled bio-aerosols in buildings. J Thorac Dis. 2018;10(Suppl 19):S2295-S2304. doi:10.21037/jtd.2018.01.24
11. Liu YY, Ning Z, Chen Y, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. 2020;86(21):2020.03.08.982637. doi:10.1101/2020.03.08.982637
12. Wei J, Li Y. Airborne spread of infectious agents in the indoor environment. Am J Infect Control. 2016;44(9):S102-S108. doi:10.1016/j.ajic.2016.06.003
13. Cowling BJ, Ip DKM, Fang VJ, et al. Aerosol transmission is an important mode of influenza A virus spread. Published online 2013:1-12. doi:10.1038/ncomms2922.Aerosol
14. Kluytmans van den Bergh MFQ, Buiting AGM, Pas SD, et al. SARS-CoV-2 infection in 86 healthcare workers in two Dutch hospitals in March 2020: a cross-sectional study with short-term follow -up. medRxiv. Published online 2020.
15. Knibbs LD, Morawska L, Bell SC. The risk of airborne influenza transmission in passenger cars. Epidemiol Infect. 2012;140(3):474-478. doi:10.1017/S0950268811000835
16. Linde KJ, Wouters IM, Kluytmans JAJW, et al. Detection of SARS-CoV-2 in Air and on Surfaces in Rooms of Infected Nursing Home Residents. Ann Work Expo Heal. 2022;XX(Xx):1-12. doi:10.1093/annweh/wxac056
17. Randall K, Ewing ET, Marr LC, Jimenez JL, Bourouiba L. How did we get here: what are droplets and aerosols and how far do they go? A historical perspective on the transmission of respiratory infectious diseases. Published online 2021. doi:10.1098/rsfs.2021.0049
18. Peng Z, Rojas ALP, Kropff E, et al. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. Environ Sci Technol. 2022;56(2):1125-1137. doi:10.1021/acs.est.1c06531
19. Tang JW, Bahnfleth WP, Bluyssen PM, et al. Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus (SARS-CoV-2) Narrative. J Hosp Infect. Published online 2021. doi:10.1016/j.jhin.2020.12.022
20. Chen W, Qian H, Zhang N, Liu F, Liu L, Li Y. Extended short-range airborne transmission of respiratory infections. J Hazard Mater. 2022;422(June 2021):126837. doi:10.1016/j.jhazmat.2021.126837
21. RIVM. Aerogene verspreiding SARS-CoV-2 en ventilatiesystemen ( onderbouwing ).
22. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One. 2012;7(4). doi:10.1371/journal.pone.0035797
23. Li Y, Huang X, Yu ITS, Wong TW, Qian H. Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air. 2005;15(2):83-95. doi:10.1111/j.1600-0668.2004.00317.x
24. Grosskopf K, Mousavi E. Bioaerosols in health-care environments. ASHRAE J. 2014;56(8):22-31.
25. Lindsley WG, Blachere FM, Thewlis RE, et al. Measurements of airborne influenza virus in aerosol particles from human coughs. PLoS One. 2010;5(11). doi:10.1371/journal.pone.0015100
26. Chen W, Zhang N, Wei J, Yen HL, Li Y. Short-range airborne route dominates exposure of respiratory infection during close contact. Build Environ. 2020;176(March):106859. doi:10.1016/j.buildenv.2020.106859
27. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of Respiratory Viral Infections. Annu Rev Virol. Published online 2020:1-19. doi:10.1146/annurev-virology-012420-022445
28. Shiu EYC, Leung NHL, Cowling BJ. Controversy around airborne versus droplet transmission of respiratory viruses: Implication for infection prevention. Curr Opin Infect Dis. Published online 2019. doi:10.1097/QCO.0000000000000563
29. Buonanno G, Stabile L, Morawska L. Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment. medRxiv. Published online 2020:2020.04.12.20062828. doi:10.1101/2020.04.12.20062828
30. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis. 2006;12(11):1657-1662. doi:10.3201/eid1211.060426
31. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11(10). doi:10.3390/v11100940
32. Doremalen N van, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. Published online 2020:1-3. doi:10.1056/NEJMc2004973
33. Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. J Hosp Infect. 2020;104(3):246-251. doi:10.1016/j.jhin.2020.01.022
34. Chin A, Chu J, Perera M, et al. Stability of SARS-CoV-2 in different environmental conditions. Lancet Infect Dis. 2020;5247(20):2020.03.15.20036673. doi:10.1016/S2666-5247(20)30003-3
35. Sandora TJ, Shih MC, Goldmann DA. Reducing absenteeism from gastrointestinal and respiratory illness in elementary school students: A randomized, controlled trial of an infection-control intervention. Pediatrics. 2008;121(6). doi:10.1542/peds.2007-2597
36. Otter JA, Donskey C, Yezli S, Douthwaite S, Goldenberg SD, Weber DJ. Transmission of SARS and MERS coronaviruses and influenza virus in healthcare settings: The possible role of dry surface contamination. J Hosp Infect. 2016;92(3):235-250. doi:10.1016/j.jhin.2015.08.027
37. Azor-Martínez E, Gonzalez-Jimenez Y, Seijas-Vazquez ML, et al. The impact of common infections on school absenteeism during an academic year. Am J Infect Control. 2014;42(6):632-637. doi:10.1016/j.ajic.2014.02.017
38. Snyder KM. Does Hand Hygiene Reduce Influenza Transmission? J Infect Dis. 2010;202(7):1146-1147. doi:10.1086/656144
39. Yang C. Does hand hygiene reduce SARS-CoV-2 transmission? Graefe’s Arch Clin Exp Ophthalmol. Published online 2020:5-6. doi:10.1007/s00417-020-04652-5
40. Santarpia JL, Rivera DN, Herrera V, et al. Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center. medRxiv. Published online 2020:2020.03.23.20039446. doi:10.1101/2020.03.23.20039446
41. Döhla M, Wilbring G, Schulte B, et al. SARS-CoV-2 in environmental samples of quarantined households. medRxiv. Published online June 2020:2020.05.28.20114041. doi:10.1101/2020.05.28.20114041
42. Fischer EP, Fischer MC, Grass D, Henrion I, Warren WS, Westman E. Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Sci Adv. 2020;6(36). doi:10.1126/sciadv.abd3083
43. Lewis D. COVID-19 rarely spreads through surfaces. So why are we still deep cleaning? Nature. 2021;590(7844):26-28. doi:10.1038/D41586-021-00251-4
44. Science Brief: SARS-CoV-2 and Surface (Fomite) Transmission for Indoor Community Environments | CDC.
45. Kitagawa H, Nomura T, Nazmul T, et al. Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination. Am J Infect Control. 2020;000:17-19. doi:10.1016/j.ajic.2020.08.022
46. Lindblad M, Tano E, Lindahl C, Huss F. Ultraviolet-C decontamination of a hospital room: Amount of UV light needed. Burns. 2020;46(4):842-849. doi:10.1016/j.burns.2019.10.004
47. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018;8(1):1-7. doi:10.1038/s41598-018-21058-w
48. Kompatscher K, Traversari R. Literatuurstudie Naar de Toepassing van Verschillende Luchtreinigingsmethoden Voor Inactivatie van Microbiologische Verontreinigingen.; 2022.
49. Ratnesar-shumate S, Williams G, Green B, et al. OUP accepted manuscript. J Infect Dis. 2020;(52281):1-9. doi:10.1093/infdis/jiaa274
Despite the lack of certainty regarding the extent to which long-range infections contribute to overall indoor infection, the following is advised from a precautionary point of view:
Reduce the potential airborne contamination risk. This means limiting the number of aerosols that may contain virus particles.
Supplying the room with sufficient fresh air is the most straight forward solution. An effective way to do this is to make good use of the ventilation system (see also www.ventilerenzogedaan.nl).
Air purification through filtration or UV-C exposure is seen as a potential complement to ventilation for reducing pathogen exposure. Barring specific situations, the application of air cleaning is not a standard solution. As of yet, air purification has not been proven effective in reducing infection rates in practice. However, many air cleaning techniques can be used to reduce the number of airborne particles, with the exception of UV-C.
It is worth noting that proper ventilation not only helps reduce the risk of virus contamination, but it also helps reducing nuisances caused by for example odors, or exposures to emissions from building materials and activities taking place in the same environment.
Based on the currently available literature, this question cannot unequivocally be answered. However, more and more literature is becoming available concerning the infection route through aerogenic transmission.1
Indications have been found in several studies that infections have occurred over longer distances via the aerogenic route. However, determining the impact of long-distance compared to shorter-distance transmission is difficult due to insufficient information regarding the circumstances surrounding the infections. Nonetheless, so-called superspreading events do suggest the occurrence of long-distance transmission.2,3 In other words, it is unknown what portion of infections occurs due to long or short distance exposure as this is situation-dependent.
Besides this, there is no consensus on the definitions of aerogenic and droplet transmission. 4 Aerosols, like respiratory droplets, are generated by respiratory activities, and are subsequently carried with the local air currents. In this way, ventilation influences the dilution and spread of aerosols. 5–18
During respiratory activities such as breathing, talking, coughing, and sneezing, aerosols (particles) and respiratory droplets of various sizes are emitted. Evaporation and airflow affect the distance particles can travel. If evaporation occurs rapidly, the droplet can cover a greater distance as it reduces in size and weight. If evaporation is slow, the droplet will settle faster, depending on its size. Relative humidity can have a significant effect on the distance larger particles, between 5 and 40 µm in diameter, can travel. These larger exhaled droplets quickly reduce in size (to about 30% of their original size), after which they can travel considerable distances, driven by air currents.19 Airflow is critical for the distances these particles can travel. Particularly smaller particles can be carried over longer distances. 20–22 Besides distance travelled, viral stability is also important. It has been demonstrated that, under laboratory conditions, 50% - 60% of active SARS-CoV-2 virus particles in 5 - 10 µm aerosols are inactivated within seconds at lower relative humidities (<45%).4,23
1. RIVM. Richtlijn COVID-19. 23 november.
2. Miller SL, Nazaroff WW, Jimenez JL, et al. Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event. Indoor Air. 2021;31(2):314-323. doi:10.1111/ina.12751
3. Peng Z, Rojas ALP, Kropff E, et al. Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks. Environ Sci Technol. 2022;56(2):1125-1137. doi:10.1021/acs.est.1c06531
4. de Crane D’Heysselaer S, Parisi G, Lisson M, et al. Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2. Pathogens. 2023;12(3):1-27. doi:10.3390/pathogens12030382
5. Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S. Transmission routes of respiratory viruses among humans. Curr Opin Virol. 2018;28:142-151. doi:10.1016/j.coviro.2018.01.001
6. Liu YY, Ning Z, Chen Y, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. 2020;86(21):2020.03.08.982637. doi:10.1101/2020.03.08.982637
7. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One. 2012;7(4). doi:10.1371/journal.pone.0035797
8. Li Y, Huang X, Yu ITS, Wong TW, Qian H. Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air. 2005;15(2):83-95. doi:10.1111/j.1600-0668.2004.00317.x
9. Grosskopf K, Mousavi E. Bioaerosols in health-care environments. ASHRAE J. 2014;56(8):22-31.
10. Lindsley WG, Blachere FM, Thewlis RE, et al. Measurements of airborne influenza virus in aerosol particles from human coughs. PLoS One. 2010;5(11). doi:10.1371/journal.pone.0015100
11. Cowling BJ, Ip DKM, Fang VJ, et al. Aerosol transmission is an important mode of influenza A virus spread. Published online 2013:1-12. doi:10.1038/ncomms2922.Aerosol
12. Chen W, Zhang N, Wei J, Yen HL, Li Y. Short-range airborne route dominates exposure of respiratory infection during close contact. Build Environ. 2020;176(March):106859. doi:10.1016/j.buildenv.2020.106859
13. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of Respiratory Viral Infections. Annu Rev Virol. Published online 2020:1-19. doi:10.1146/annurev-virology-012420-022445
14. WHO. Modes of transmission of virus causing COVID-19 : implications for IPC precaution recommendations. Sci Br WHO. 2020;(March):10-12. doi:10.1056/NEJMoa2001316.5.
15. Shiu EYC, Leung NHL, Cowling BJ. Controversy around airborne versus droplet transmission of respiratory viruses: Implication for infection prevention. Curr Opin Infect Dis. Published online 2019. doi:10.1097/QCO.0000000000000563
16. Buonanno G, Stabile L, Morawska L. Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment. medRxiv. Published online 2020:2020.04.12.20062828. doi:10.1101/2020.04.12.20062828
17. Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis. 2006;12(11):1657-1662. doi:10.3201/eid1211.060426
18. Judson SD, Munster VJ. Nosocomial transmission of emerging viruses via aerosol-generating medical procedures. Viruses. 2019;11(10). doi:10.3390/v11100940
19. Mikhailov E, Vlasenko S, Niessner R, Pöschl U. Interaction of aerosol particles composed of protein and salts with water vapor: hygroscopic growth and microstructural rearrangement. Atmos Chem Phys Discuss. 2003;3(5):4755-4832. doi:10.5194/acpd-3-4755-2003
20. Liu L, Li Y, Nielsen P V., Wei J, Jensen RL. Short-range airborne transmission of expiratory droplets between two people. Indoor Air. 2017;27(2):452-462. doi:10.1111/ina.12314
21. Schijven J, Vermeulen LC, Swart A, et al. Exposure assessment for airborne transmission of SARS-CoV-2 via breathing , speaking , coughing and sneezing. Published online 2020.
22. Tellier R, Li Y, Cowling BJ, Tang JW. Recognition of aerosol transmission of infectious agents: A commentary. BMC Infect Dis. 2019;19(1):1-9. doi:10.1186/s12879-019-3707-y
23. Oswin HP, Haddrell AE, Otero-Fernandez M, et al. The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment. Proc Natl Acad Sci U S A. 2022;119(27):1-11. doi:10.1073/pnas.2200109119
For the proper use of a ventilation system, please refer to https://www.ventilerenzogedaan.nl . This website provides 5 basic tips on how best to handle a ventilation system to ensure proper use of the ventilation facilities. Additionally, users can create a so-called ‘ventilatiekaart’ or ventilation guide, which shows information on how to best use the ventilation facilities present in the room. By placing this ventilation guide by the entrance to the room, users can quickly understand the correct use of the facilities. The publication ‘Ventilatie in relatie tot COVID-19 en een goede binnenluchtkwaliteit’ can be used to test the amount of ventilation in more detail .
 Heumen S van, Weerdt C van der, Jacobs P, Traversari R, Hinkema M. Achtergronddocument Handreiking Ventileren Zo Gedaan. Delft, The Netherlands; 2022.
 Binnenklimaattechniek. Ventilatie in Relatie Tot COVID-19 En Een Goede Binnenluchtkwaliteit; 2021.